Magnetic resonance (MR) imaging is an imaging method used in many fields of medicine for the purpose of examination and diagnosis. It is based on the physical effect of nuclear spin resonance. For the purpose of recording MR signals, a basic magnetic field is established within an examination region by means of a basic field magnet, thereby aligning the magnetic moments of nuclei such as hydrogen nuclei H-1 or nitrogen nuclei N-14, for example.
The nuclear spins can be deflected or excited out of the aligned position parallel with the basic magnetic field, i.e. the position of rest, or out of another state, by means of irradiation using high-frequency (HF) pulses. During the relaxation into the position of rest, a decay signal is generated which can be inductively detected as an MR signal by one or more HF receive coils. For example, selective dephasing and rephasing of the nuclear spins by means of switching gradient fields in a suitable manner can generate an MR signal. Such an effect is used in so-called gradient echo MR recording sequences.
As a result of establishing a layer selection gradient when the high-frequency pulses are irradiated, nuclear spins are only excited in an examination object layer in which the resonance condition is satisfied due to the local magnetic field strength. Further spatial encoding can be achieved by establishing at least one phase coding gradient and one frequency coding gradient during the readout. It is thereby possible to obtain MR signals in a spatially resolved manner from a plurality of layers of a person being examined. Using suitable representation methods, a three-dimensional (3D) mapping of a specific region of the person being examined can be provided in this way for the purpose of diagnosis. A typical spatial resolution of the MR imaging in this context can be 1 mm in all three spatial directions, for example. Such a spatially distributed imaging point is referred to as a voxel.
For the purpose of MR imaging, a patient is generally moved into the interior of the basic field magnet on a couch or a table. In order to improve the MR imaging, use is also made of HF local coils which are placed in the immediate vicinity of the patient. The imaging space therefore contains not only the patient, but also other parts such as the couch and the coils, these being made from the widest variety of materials. However, these materials can likewise produce an image as they contain nuclei that are also used for the MR imaging.
Imaging properties of materials that are situated inside the examination region which is used for MR imaging can give rise to artifacts in the MR images. Such artifacts can result in incorrect diagnosis or render the image diagnostically unusable. Relatively few materials are known which exhibit reduced visibility in MR imaging in empirical tests. The number of usable materials is limited because, in addition to reduced visibility in the MR imaging, usability within an MR installation is also governed by other criteria such as little or no electrical conductivity and little or no magnetic susceptibility, for example.
Since it is not possible to utilize significantly less expensive plastic materials, for example, this can result in higher costs in the manufacture of components for use in the MR installation. Furthermore, e.g. such soft and flexible plastic materials as are found in various fields of everyday life cannot be used because as a solid material they do not exhibit reduced visibility in the MR imaging. This can result in reduced comfort and limited design freedom in the utilization and/or manufacture of components for use in an MR installation. Furthermore, it may not be possible to utilize materials that have particularly good working properties or are particularly robust or stable. This can result in reduced reliability or a reduced service life of the components to be used in the MR installation.
For example, U.S. Pat. No. 7,604,875 B2 discloses techniques which allow the magnetic susceptibility of support materials to be matched to fixed predefined values by means of adding paramagnetic and/or diamagnetic substances. However, the techniques disclosed therein relate to the mitigation of a susceptibility mismatch, as a result of which the static magnetic field varies on a length scale of several centimeters and deviates from the desired value of the basic magnetic field. This can result in the occurrence of displacements or spatial distortions in MR images, for example, or adversely affect the quality of spectral fat saturation techniques. However, the visibility of the materials in the MR imaging is not affected.